1. Field of the Invention
The present invention relates to a macromolecular structure including hyperbranched macromolecules having a hole conductivity or an electron conductivity, a functional device using the same, a transistor whose semiconductor layer includes organic macromolecules, and a display apparatus using the same.
2. Description of the Related Art
In recent years, active matrix liquid crystal display apparatuses using active devices such as thin film transistors (TFTs) have been used as monitors in notebook personal computers, desktop personal computers, workstations, etc., and as LCD televisions, etc., for their advantageous features such as providing image qualities as high as, or higher than, those of CRTs, consuming less power and taking up smaller spaces than CRTs. However, active matrix liquid crystal display apparatuses are more expensive than CRTs, and a further decrease in the price is called for so that active matrix liquid crystal display apparatuses can become widespread.
Active researches have been undertaken also for active matrix organic EL devices in which organic electroluminescence light-emitting devices (organic EL devices or OLEDs) are driven by using active devices, and a decrease in the price is called for also for active devices of organic EL devices.
As one approach to decrease the price, it has been proposed in the art to employ, as active devices, field effect transistors (organic FETs or organic TFTs) using an organic thin film semiconductor, which can advantageously be produced by a relatively simple method.
At present, a plasma chemical vapor deposition (CVD) apparatus for producing an insulating layer or a semiconductor layer of an amorphous silicon or polysilicon TFT and a sputtering apparatus used for forming electrodes thereof are expensive. Moreover, a CVD method uses a high deposition temperature of 230° C. to 350° C., and requires frequent maintenance such as cleaning, resulting in a low throughput. As compared with a CVD apparatus and a sputtering apparatus, an application apparatus, an inkjet apparatus, and the like, for producing an organic FET, etc., are less expensive, use lower deposition temperatures, and are easy to maintain. Therefore, a significant decrease in the cost can be expected when organic FETs are used in a display apparatus such as a liquid crystal display apparatus or an organic EL device.
A typical organic TFT includes a transparent substrate made of a glass, or the like, a gate electrode, a gate insulating layer, a drain electrode, a source electrode, and an organic semiconductor film. The gate voltage is changed to control the amount of charge at the interface between the gate insulating layer and the organic semiconductor film to be excessive or insufficient, thereby changing the level of the drain current flowing between the drain electrode and the source electrode, thus performing a switching operation.
Japanese Laid-Open Patent Publication No. 63-076378 discloses production of an organic TFT by using a film of polythiophene or a polythiophene derivative as the organic semiconductor film. Moreover, Yen-Yi Lin, David J. Gundlach, Shelby F. Nelson, and Thomas N. Jackson, IEEE Transaction on Electron Device, Vol. 44, No. 8 p. 1325 (1997) discloses production of an organic TFT by using pentacene.
In a case where pentacene is used, it is necessary to use a vapor deposition method, and it is thus necessary to improve the degree of crystallinity, etc., in order to improve the characteristics. It has also been studied in the art to use a pentacene derivative to provide solubility in order to improve the workability. However, sufficient characteristics have not been obtained.
Moreover, an organic semiconductor using polythiophene, a polythiophene derivative or a thiophene oligomer has a desirable formability and can easily be formed into a thin film by using an electrolytic polymerization method, a solution application method, or the like, and it has been researched in the art for practical applications. However, sufficient characteristics have not yet been obtained.
As described above, a conductive macromolecule (including a semiconductive macromolecule) has a desirable formability and can easily be formed into a thin film, and it has been researched in the art for its application to various functional devices such as a light-emitting device, a solar cell and a photoelectric conversion device, in addition to an organic FET device.
These functional devices have a semiconductor-semiconductor interface, a semiconductor-conductor interface, or the like, and their functions are exerted by, for example, carriers such as holes and electrons passing through these interfaces. It is important for such an interface that the opposing members are in close contact with each other across a large area. However, there are limits to increasing the interface area, and such an interface is often subject to a strong electric field or stress and is prone to degradation and peeling. This results in problems such as a decrease in durability due to interface degradation, and a decrease in response speed and output due to an insufficient interface area.
In view of this, U.S. Pat. No. 5,563,424 discloses a technique using a three-dimensional cocontinuous phase-separated structure of a polymer blend-type polymer alloy in order to increase the interface area. Moreover, Japanese Laid-Open Patent Publication No. 2000-286479 discloses a technique using a copolymerized-type polymer alloy, in which the interface durability is improved by forming a chemical bond at the interface.
Moreover, in recent years, hyperbranched macromolecules such as dendrimers and hyperbranched polymers have been attracting public attention. Dendrimers and hyperbranched polymers have characteristic features such as being amorphous, being soluble in organic solvents, and having many terminals to which functional groups can be introduced. In view of this, L. L. Miller, et al.; J. Am. Chem. Soc., 1997, 119, 1005 shows that a polyamide dendrimer having, at a branch terminal, a 1,4,5,8-naphthalenetetracarbonate diimide residue with quaternary pyridinium salt bound thereto has an isometric electron conductivity and that the conductivity is brought about by π-electron interaction due to spatial overlap between branch terminal structures. Moreover, Japanese Laid-Open Patent Publication No. 2000-336171 discloses a dendrimer and a photoelectric conversion device using the same, in which the dendrimer has a hole (positive hole)-conducting structure at a branch terminal, and the dendrimer is produced by using dendrons that do not include a π-electron conjugated system including a carbonyl group and a benzene ring.
Hereinafter, a conductive macromolecule that does not include a hyperbranched macromolecule, such as a conjugated macromolecule, will be referred to as a “conventional conductive macromolecule”.
However, in a functional device using a conventional conductive macromolecule as described above, a high charge conductivity is exhibited in the direction in which the macromolecular chain is oriented, whereby it is influenced by the structure of the macromolecule.
Furthermore, many of the conventional conductive macromolecules are generally rigid and insoluble/non-meltable. In view of this, a polymer derivative or an oligomer to which a side chain is introduced for providing or improving meltability or solubility has been used (e.g., Japanese Laid-Open Patent Publication Nos. 4-133351, 63-76378, 5-110069, 7-126616, 8-18125 and 10-92576).
However, when a side chain is introduced, the flexibility of the macromolecular chain is increased, and the glass transition temperature is exhibited within the operating temperature range. As a result, thermochromism occurs due to micro-Brownian motion, and the π-electron conjugation length is shortened, thereby lowering the characteristics stability against temperature. The use of an oligomer results in problems such as a decrease in reliability. Moreover, with a system using an oligomer, sufficient mobilities have not been obtained, and it is necessary to increase the degree of polymerization, or to take measures such as to improve the alignment of the conductive organic compound by using an alignment film as described in Japanese Laid-Open Patent Publication No. 7-206599, etc. Furthermore, a conjugated macromolecule is easily influenced by oxygen or water, and is prone to degradation.
Moreover, in the device disclosed in Japanese Laid-Open Patent Publication No. 2000-336171, only the charge-conducting portion is formed by using a dendrimer, and the charge-generating portion is formed by using a conventional conductive macromolecule. Therefore, while the characteristics of the charge-conducting portion formed from a dendrimer is improved, characteristics such as interlayer energy movement and interlayer carrier movement are substantially the same as those of a device using a conventional conductive macromolecule, thus resulting in problems such as a poor durability and peeling at the interface.
As described above, sufficient characteristics have not been obtained with conventional organic functional devices such as organic FET devices, and they have problems such as a poor stability and a short operating lifetime.
The present invention, which has been made in view of the above, has an object to improve the characteristics and/or reliability of a functional device using a conductive macromolecule, and to provide a macromolecular structure that can suitably be used in such a functional device. Moreover, another object of the present invention is to provide a display apparatus using such an organic functional device.